ON THE TOWN: It was party-time at actress Patti D'Arbanville's Santa Monica home last weekend, as a host of pop celebrities turned out for Pamela Des Barres' birthday. Des Barres had lots to celebrate--the former member of the GTO's just finished her first book, "I'm With the Band," a chronicle of her days as a rock 'n' roll scene-maker (and scene-stealer) that will be out next spring from William Morrow & Co. Special guests included Madonna (sans Sean Penn), Bruce Willis, Julian Lennon, ex-Duranie Andy Taylor, ex-Sex Pistol Steve Jones, Moon and Dweezil Zappa and rock toastmaster Rodney Bingenheimer, who escorted the members of Bananarama. An added highlight was a congratulatory midnight phone call from D'Arbanville's ex, pop-cop Don Johnson, who has plenty to celebrate about himself--his single, "Heartbeat," just cracked the Billboard Top 20. . . . And watch for an all-acoustic benefit concert Oct. 13 at San Francisco's Shoreline Amphitheatre to raise funds for the Bridge School, a Bay Area-based educational program for severely physically handicapped children. The event, produced by Bill Graham, will feature sets by Bruce Springsteen, Don Henley, Tom Petty, Robin Williams, Nils Lofgren and Neil Young, whose wife, Peggy, was a key organizer of the event.